This invention relates generally to a method for marking petroleum hydrocarbons with substituted anthraquinone compounds for subsequent identification.
1,4-bis-alkylamino-5,8-dihydroxyanthraquinones were disclosed in Japanese Pat. App. Ser. No. 2000-263953 for use in a thermal transfer recording method. This reference, however, does not suggest a method for marking petroleum hydrocarbons.
A variety of dyes has been used to mark petroleum hydrocarbons. Some of these are expensive, difficult to prepare, or unstable. Combinations of dyes can be used as digital marking systems, with the ratios of amounts forming a code for the marked product. Additional compounds useful as petroleum markers would be desirable to maximize the available codes. The problem addressed by this invention is to find additional markers useful for marking petroleum hydrocarbons.